Blender Render Too Dark
Your scale is very large.

This means that lights need a lot more power in order to light the objects.

For example a 100W light bulb will light a stadium, you need lots of light.

So to fix this, either scale your model to life size, or increase the values to something scary.

Also looking at your backdround color you can increase the environmental lighting by making your background white (I suggest using the RGB input node rather than the brightness contrast node).  You can always increse the luminance of the background color to modify the envronmental lighting level.

This is a simple render with only 2 lamps, a very slight background.  There's an issue with your whiskey glasses, the mesh needs some work, but you get the idea.  Start with no lights, setup your background, then highlight with some lighting for mood.



And this is the same lighting with a white background (same strength = 100 )